Key Points
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Cats with worms show symptoms like vomiting, diarrhea, a large abdomen, weight loss, and lethargy.
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The most common internal parasites are roundworms, tapeworms, and hookworms, but less common ones like Giardia or Isospora also affect some cats.
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Praziquantel, pyrantel, piperazine, and fenbendazole are commonly used to combat these parasites.
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Broad-spectrum dewormers are available without a prescription from your veterinarian, and they range from Bayer’s Drontal to the Hartz UltraGuard Rid Worm Liquid.
As a cat owner, keeping your cat healthy is always a concern. Internal and external parasites affect a cat’s health and cause various complications, from anemia to digestive distress. This article looks at the most common medications used for treating internal parasites of cats and why these dewormers work differently for various worm types.
When Does Your Cat Need a Dewormer?
Whether they have intestinal parasites or not, deworming your cat is always the best idea. If you let your cat go outdoors, chances are they've already picked up worms from other animals they interact with or from the environment. Outdoor pets carry external and internal parasites regularly and transmit them to other animals. You may inadvertently bring home larvae or eggs on your shoes, so indoor cats aren’t fully protected against these parasites either.
Vets recommend that you deworm your cat as soon as you adopt them. Some parasites threaten human health, such as Toxoplasma species, so it’s better to be safe than sorry. While there are multiple types of intestinal parasites, the best solution is to give your cat a broad-spectrum de-worming medication.
A cat with intestinal parasites may show these symptoms:
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Vomiting or diarrhea
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Constipation
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A dry and dull coat
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Excessive grooming of their nether region
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A large abdomen
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Weight loss
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An unusual increase in the cat’s appetite
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Pale gums
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Lethargy
Deworming your cat allows them to feel better on the whole and live a healthier and happier life. When a cat has a severe parasite population in their body, the worms deplete them of nutrients that otherwise provide sustenance for your pet. This is why kittens are often ravenous, but despite the food they get, they still seem unhealthy.
Furthermore, parasites can lead to serious nutritional deficiencies, including anemia, especially for vulnerable seniors, kittens, and pregnant cats. Some worms cause life-threatening intestinal blockages, no matter the cat’s age.
Different Types of Worms
There are three types of internal parasites that felines are vulnerable to — tapeworms, roundworms, and hookworms. Kittens tend to get roundworms and tapeworms more often than hookworms, especially if their mother is not a carrier for hookworms.
Less common parasites are protozoans, such as coccidial infections — caused by the Isospora species –and dimorphic parasites, such as Giardia. The main difference with these parasites is that your pet’s poop does not reveal eggs or larvae. Therefore, even though they experience diarrhea, dehydration, vomiting, and other symptoms, cat owners often believe that the health issue is unrelated to parasites.
A fecal examination — available at most large veterinary clinics — reveals what type of worms your cat has. Veterinary parasitologists at vet colleges perform the exam, as well. While broad-spectrum medications are more effective for tapeworms, roundworms, and hookworks, medications like fenbendazole and metronidazole are better for Giardia and Isospora species.
The Most Common Medications for Worms in Cats
According to Auburn University professor Dr. Byron Blagburn, MS, PhD, “[A]lthough effective anthelmintics have been available for many years, worldwide prevalences of feline internal parasites do not appear to have changed significantly.”
As a responsible cat owner, you want to make sure your pet does not become a victim of internal parasites. Most over-the-counter (OTC) medications for parasites have been regulated for years and are available in pet shops and online marketplaces. Some may require a prescription from your vet, depending on your area. Below are the most commonly used active ingredients in deworming medication are described below.
Praziquantel
Praziquantel is commonly used in both dogs and cats for treating tapeworms. This medication acts by paralyzing the tapeworm and rendering its cells incapable of holding onto calcium. Once the parasite dies, the cat’s body merely digests and safely eliminates it through the feces. Some cats experience adverse reactions to praziquantel, such as excessive salivation, diarrhea, and vomiting, but they recover in 24 to 48 hours.
Pyrantel Pamoate
Pyrantel is used to kill both hookworms and roundworms. While this medication has been used for decades and is mostly safe, its use depends on the severity of the infection. If a cat has a large population of either roundworms or hookworms and they die inside the gut after being paralyzed by the medication, this could lead to a toxic reaction. Always follow your vet’s recommendation in terms of dosage.
Piperazine
Although piperazine proves its worth when killing roundworms, it's ineffective for treating hookworms. A correct diagnosis is necessary if you suspect that your cat has hookworms. Still, any broad-spectrum medication containing pyrantel, praziquantel, and piperazine is effective against tapeworms, roundworms, and hookworms. High doses result in side effects such as nausea, muscle tremors, and loss of balance.
Fenbendazole
An August 2023 article by Sploot Veterinary Care notes that fenbendazole is the medication used for treating Giardia in cats and dogs. To treat Giardia, you need a prescription, as vets recommend a combination of fenbendazole and metronidazole. Although there is no approved drug in the United States for treating Giardia in pets, this combo is effective. Fenbendazole is commercially sold as Safe-Guard or Panacur. It has side effects, such as vomiting, drooling, or lethargy, but these symptoms subside in less than 48 hours following administration.
Are Natural Dewormers an Option for Your Cat?
Sometimes cat owners want to avoid pharmacological solutions and opt for natural remedies to combat worms. However, herbal blends are rarely effective. If herbal capsules contain natural compounds such as garlic, cloves, ginger, or walnuts, they'll do nothing to kill internal parasites, no matter their type.
The other natural solution pet owners resort to is diatomaceous earth. This organic insecticide protects animals against external parasites, but it's not approved for use in cats and is thus unregulated. At best, diatomaceous earth may help your cat expel the parasites, but it won't kill the larval forms or eggs. Your vet won't be able to advise you on dosage.
Best Cat Dewormers
There are multiple names for both OTC dewormers and those that require a prescription, and vets rely on many of them. Some topical solutions kill fleas and specific intestinal parasite types — mostly roundworms and hookworms — such as Revolution Plus, which contains selamectin. Milbemax is popular with other vets, as it's also effective for the same three worm types and is safe for kittens as young as six weeks.
While there's no such thing as a cat dewormer for all worms, as each species calls for a different medication, you do not need a prescription for broad-spectrum ones. Below are some of the best OTC cat dewormers available.
Bayer Drontal
Bayer's Drontal is the best cat dewormer if you don't have a vet prescription. Since it's a broad-spectrum medication containing both pyrantel and praziquantel, it works by killing three types of different internal parasites — hookworms, roundworms, and tapeworms. It's safe to administer to kittens if you stick to your vet’s recommendations and calculate the dosage depending on their age and weight. However, don't give it to cats whose weight is under 1.5 pounds.
As is the case with other dewormers, Drontal does not prevent reinfection. In other words, if you let your cat go outside, they consistently pick up parasites from other animals, so treating them regularly is necessary.
Although rare, some side effects of Bayer's Drontal occur in certain animals, including loss of appetite, excessive drooling, vomiting, and diarrhea. Cats with a large internal parasite population may experience lethargy. These symptoms subside in less than 24 to 48 hours.
by Hartz
Hartz UltraGuard Rid Worm Liquid
If your cat has roundworm, a reliable option is Hartz UltraGuard Rid Worm Liquid. Some cats don't like to take capsules or tablets, but Hartz UltraGuard's liquid form makes administration easy. Either mix it with food or water or drop it right into your cat's mouth. Keep in mind this dewormer only works for roundworms, so it's not recommended for cats diagnosed with other parasites.
As the dosage is essential, especially for young cats, the manufacturing company recommends measuring the product using a teaspoon with a capacity of up to five mL. This dosage is appropriate for cats with a body weight of five pounds. This medication should not be given to pets younger than six weeks of age.
While this medication is available for purchase over the counter, consult your veterinarian if your cat is debilitated or has been showing signs of general malaise or dehydration. The brand recommends repeating the treatment 14 days after the first dose, but ask your vet to be on the safe side as roundworm species have different hatching schedules.
by Elanco
Elanco Tapeworm Dewormer
Elanco Tapeworm Dewormer kills two common types of tapeworms — the Taenia and Dipylidium species. Administer one of these praziquantel tablets to a cat weighing five to 11 pounds. Half a tablet is recommended for cats and kittens weighing under four pounds. If you have a cat over 11 pounds, give them one and a half tablets.
Although the Elanco Tapeworm Dewormer is an effective way to combat tapeworms, if you're unsure of the type of intestinal parasites your cat has, opt for a broad-spectrum solution such as Drontal.
Deworming Your Cat Protects You and Your Pet
Pet parasites are a reality; unfortunately, they're not going anywhere. There are multiple medications for different species of parasites, and many are available without a prescription from your veterinarian. Protecting your cat protects your entire family.
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